1. 16.216 ECE Application Programming
Instructor: Dr. Michael Geiger
Spring 2014
Lecture 6:
Output formatting
If statements

2. ECE Application Programming: Lecture 6
Lecture outline
Announcements/reminders
Program 2 due 2/5
Today’s lecture
Output formatting
Intro to if statements
5/11/2018
ECE Application Programming: Lecture 6

3. Formatted output: field width
Specifying field width (min # characters) (assume n = 12):
printf(“%10d”, n);  (8 spaces, then number 12)
To left justify value in field, use – flag before width
printf(“%-10d”, n);  12________ (Number 12, then 8 spaces)
To force the sign to show, use + flag before width
printf(“%+10d”, n); 
(7 spaces, a plus sign, then number 12)
To place 0s before the value, use 0 flag before width
printf(“%010d”, n); 
printf(“%+010d”, n); 
printf(“%-010d”, n);  12________
To use a variable to specify field width, use * as the width
printf(“%*d”, n, n); 
(Field width = 12  10 spaces, then the number 12)
Field width never truncates
printf(“%1d”, n);  still prints 12
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ECE Application Programming: Lecture 6

4. Formatted output: precision
For examples, int n = 12; double x = 3.754
Specifying precision:
# chars after decimal point for FP (%f, %lf)
Rounds last digit
printf(“%.6lf”, x); 
printf(“%.1lf”, x);  3.8
printf(“%.0lf”, x);  4
Minimum # chars for integer (%d, %i, %u, %x)
Does not truncate; will pad with leading 0s
printf(“%.1d”, n);  12
printf(“%.3d”, n);  012
Max # chars for string (%s)
printf(“%.5s”, “one”);  one
printf(“%.5s”, “one two”);  one t
No effect for char (%c)
As with field width, can use * to specify that field width is a variable
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ECE Application Programming: Lecture 6

5. Formatting and scanf()
Formatting specified above used only for printf()
Have very different meaning for scanf()
printf("%3d", x)  print x w/field width of 3
scanf("%3d", &x)  read 3 characters into x
If you enter: 12  x = 12
If you enter: 1234  x = 123
Bottom line: you probably don’t want to “format” your input!
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ECE Application Programming: Lecture 6

6. ECE Application Programming: Lecture 6
Note
The next three slides contain full specification for printf() flags, field width, and precision
Read on if you want lots of details; skip these slides if the previous ones were sufficient
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ECE Application Programming: Lecture 6

7. printf format specifications
General form: % [flags] [width] [.precision] [ { h | l | I64 | L } ] type
flag
meaning
default -
Left align the result within the given field width
Right align +
Prefix the output value with a sign (+ or -) if the output value is of a signed type.
Sign appears only for negative signed values (-)
If width is prefixed with 0, zeros are added until the minimum width is reached. If 0 and - appear, the 0 is ignored.
No padding (actually space padding)
blank
Prefix the output value with a blank if the output value is signed and positive; the blank is ignored if both the blank and + flags appear.
No blank appears #
When used with the o, x, or X format, the # flag prefixes any nonzero output with 0, 0x, or 0X, respectively. Ignored when used with c, d, i, u, or s.
No prefix
When used with the e, E, or f format, the # flag forces the output value to contain a decimal point in all cases.
Decimal point appears only if digits follow it.
When used with g or G format, forces the output value to contain a decimal point in all cases and prevents the truncation of trailing zeros.
Decimal point appears only if digits follow it. Trailing zeros are truncated.
This slide adapted from information in MSDN Library
5/11/2018
ECE Application Programming: Lecture 6

8. printf format specifications
General form: % [flags] [width] [.precision] [ { h | l | I64 | L } ] type
The width argument is a nonnegative decimal integer controlling the minimum number of characters printed. If the number of characters in the output value is less than the specified width, blanks are added to the left or the right of the values — depending on whether the – flag (for left alignment) is specified — until the minimum width is reached.
Notes:
If width is prefixed with 0, zeros are added until the minimum width is reached (not useful for left-aligned numbers).
The width specification never causes a value to be truncated. If the number of characters in the output value is greater than the specified width, or if width is not given, all characters of the value are printed (subject to the precision specification).
5/11/2018
ECE Application Programming: Lecture 6
This slide adapted from information in MSDN Library

9. printf format specifications
General form: % [flags] [width] [.precision] [ { h | l | I64 | L } ] type
typ
meaning
default c
The precision has no effect
character is printed
d,i, u,o, x,X
The precision specifies the minimum number of digits to be printed. If the number of digits in the argument is less than precision, the output value is padded on the left with zeros. The value is not truncated when the number of digits exceeds precision
Default precision is 1.
e,E
The precision specifies the number of digits to be printed after the decimal point. The last printed digit is rounded.
Default precision is 6; if precision is 0 or the period f
The precision value specifies the number of digits after the decimal point. If a decimal point appears, at least one digit appears before it. The value is rounded to the appropriate number of digits.
(.) appears without a number following it, no decimal point is printed.
g,G
The precision specifies the maximum number of significant digits printed.
Six significant digits are printed, with any trailing zeros truncated.
s,S
The precision specifies the maximum number of characters to be printed. Characters in excess of precision are not printed.
Characters are printed until a null character is encountered.
5/11/2018
ECE Application Programming: Lecture 6
This slide adapted from information in MSDN Library

10. ECE Application Programming: Lecture 6
examples - printf()
float a=67.49,b= ; printf("Price:█%10f█%10f\n",a,b); printf("%8.2f█%8.4f█%5.1f█%7.5f\n",a,a,b,b); printf("a=%5.5f,█b=%0.2f\n",a,b);
Printed:
print position Price:██ ███ columns ███67.49██ ██10.0█ to 35 a= ,█b=10.00
Note: On last line of output, the actual value was output; the printf routine overrode the specified width.
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ECE Application Programming: Lecture 6

11. ECE Application Programming: Lecture 6
examples - printf()
float a=67.49,b= ; int i=184,j=-51; double x= , y=-22.33;
printf("%7.1lf%5d%8.2f\n",y,i,a); printf("%13.2f%4d%9.2lf\n",b,j,x); //changed
Printed:
print position
columns to 35
Notes: d indicates decimal integer f indicates float lf (that’s lower case L and f) indicates double (for double output, f OK too; not OK for input)
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ECE Application Programming: Lecture 6

12. ECE Application Programming: Lecture 6
printf() examples
printf("vv% dww%-dxx%+dyy%dzz\n",-12,-34,-56,-78);
..../ / / / <= ruler vv-12ww-34xx-56yy-78zz
printf("vv% dww%-dxx%+dyy%dzz\n",12,34,56,78);
..../ / / / <= ruler vv 12ww34xx+56yy78zz
printf("vv% 5dww%-5dxx%+5dyy%5dzz\n",-12,-34,-56,-78);
..../ / / / <= ruler vv -12ww-34 xx -56yy -78zz
printf("vv% 5dww%-5dxx%+5dyy%5dzz\n",12,34,56,78);
..../ / / / <= ruler vv 12ww34 xx +56yy 78zz
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ECE Application Programming: Lecture 6

13. ECE Application Programming: Lecture 6
printf() examples
printf("v% 05dw%-05dx%+05dy%05dz\n",-12,-34,-56,-78);
..../ / / / <= ruler v-0012w-34 x-0056y-0078z
printf("v% 05dw%-05dx%+05dy%05dz\n",12,34,56,78);
..../ / / / <= ruler v 0012w34 x+0056y00078z
printf("v%7.3dw% 7.3dx%-7.3dy%+7.3dz\n",-12,-34,-56,-78);
..../ / / / <= ruler v w x y z
print("v%7.3dw% 7.3dx%-7.3dy%+7.3dz\n", 12, 34, 56, 78);
..../ / / / <= ruler v w x y z
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ECE Application Programming: Lecture 6

14. ECE Application Programming: Lecture 6
printf() examples
printf("w%7.2fx%7.2fy%7.2fz\n",-1.234,-3.456,-5.6);
..../ / / / <= ruler w x y z
printf("w%7.2fx%7.2fy%7.2fz\n", 1.234, 3.456, 5.6);
..../ / / / <= ruler w w y z
printf("w%7.2fx%7.2f\n", , );
..../ / / / <= ruler w x z
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ECE Application Programming: Lecture 6

15. Example: Formatted output
Assume int x = 123; float y = 4.56; double z =
What does each of the following lines print?
printf("%4d %5f %6lf\n", x, y, z);
printf("%.4d %.4f %.4lf\n",
x, y, z);
printf("%08d %-7.1f %+-4.1lf !\n",
The second and third specifiers have precision of 1
One is a float (%f), the other is a double (%lf)
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ECE Application Programming: Lecture 6

16. ECE Application Programming: Lecture 6
Example solution
printf("%4d %5f %6lf\n",
x, y, z);
 █123█ █
printf("%.4d %.4f %.4lf\n",
 0123█4.5600█7.8999
printf("%08d %-7.1f %+-4.1lf!\n",
 █4.6█████+7.9█!
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ECE Application Programming: Lecture 6

17. Example: Formatted output
Write a short code sequence to do each of the following:
Print three integers—x, y, and z
Use field widths of 10, 20, and 30, respectively
Put an extra space between each field
Show the signs of all values and left justify them
Print four doubles—d1, d2, d3, d4
Use field widths of 7 for all values
Show 1, 2, 3, and 4 places after the decimal point, respectively
Given three variables—int w, p; double var;
Read values for w and p from the input
Print var using field width w and precision p
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ECE Application Programming: Lecture 6

18. ECE Application Programming: Lecture 6
Example solution
Print three integers—x, y, and z
Use field widths of 10, 20, and 30, respectively
Put an extra space between each field
Show the signs of all values and left justify them
printf(“%+-10d %+-20d %+-30d\n”, x, y, z);
Print four doubles—d1, d2, d3, d4
Use field widths of 7 for all values
Show 1, 2, 3, and 4 places after the decimal point, respectively
printf(“%7.1lf %7.2lf %7.3lf %7.4lf\n”,
d1, d2, d3, d4);
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ECE Application Programming: Lecture 6

19. Example solution (cont.)
Given three variables—int w, p; double var;
Read values for w and p from the input
Print var using field width w and precision p
scanf(“%d %d”, &w, &p);
printf(“%*.*lf\n”, w, p, var);
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ECE Application Programming: Lecture 6

20. ECE Application Programming: Lecture 6
Decisions
Recall that flowcharts can include decisions
Conditionally execute some path
May want to:
Only perform operation if condition is true:
A = 0?
TRUE
FALSE
A = 0?
TRUE
X = x + 1
FALSE
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ECE Application Programming: Lecture 6

21. ECE Application Programming: Lecture 6
Decisions (cont.)
May want to:
Perform one operation if condition is true, another if false:
A = 0?
TRUE
X = x + 1
FALSE
X = x - 1
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ECE Application Programming: Lecture 6

22. ECE Application Programming: Lecture 6
Decisions (cont.)
May want to:
Check multiple conditions, in order
A = 0?
TRUE
X = x + 1
FALSE
B=1?
TRUE
X = x - 1
FALSE
X = 0
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ECE Application Programming: Lecture 6

23. ECE Application Programming: Lecture 6
if statements
Frequently want to conditionally execute code
Range checking
Error checking
Different decisions based on input, or result of operation
Basic conditional execution: if statement
Form:
if (<expression>)
<statement>
[ else brackets show
<statement> ] else is optional
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ECE Application Programming: Lecture 6

24. ECE Application Programming: Lecture 6
if statements (cont.)
<expression> can be any valid expression
Considered “false” if 0, “true” if nonzero
Can use comparisons:
Greater than/less than: > <
e.g. if (a < b)
Greater than or equal/less than or equal: >= <=
e.g. if (x <= 20)
Equal/not equal: == !=
e.g. if (var == 10)
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ECE Application Programming: Lecture 6

25. ECE Application Programming: Lecture 6
if statements (cont.)
<expression> can be any valid expression
Can combine multiple conditions using
Logical AND: &&
Logical OR: ||
e.g. if ((x < 3) && (y > 5))
Always put each condition in parentheses
Can test inverse of condition using logical NOT: !
e.g. if (!(x < 3))  equivalent to if (x >= 3)
These operators: not bitwise operators!
A & B is a bitwise operation
A && B has only 2 possible results: 0 or “non-zero”
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ECE Application Programming: Lecture 6

26. ECE Application Programming: Lecture 6
if statements (cont.)
<statement> can be one or more lines
If just one line, no additional formatting needed
if (x < 3)
printf(“x = %d\n”, x);
If multiple lines, statement is block enclosed by { }
if (x < 3) {
x = x + 3; }
else part is optional—covers cases if condition is not true
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ECE Application Programming: Lecture 6

27. ECE Application Programming: Lecture 6if
if (a > b) big = a; else big = b;
if (a+6*3-43) printf("wow is this not cool"); else printf("this is not cool");
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ECE Application Programming: Lecture 6

28. ECE Application Programming: Lecture 6
if (common pitfalls)
a single equals means ASSIGN.
a double equal must be used to check for equality.
x=12345;
if (x=3) { printf("x is 3\n"); } else { printf("x is not 3\n"); }
This code will ALWAYS print: x is 3
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ECE Application Programming: Lecture 6

29. ECE Application Programming: Lecture 6
if (example)
void main(void) { float a,b,c,disc; : scanf("%f %f %f",&a,&b,&c); if (a==0) { // statements } else { disc = b*b-4*a*c; if ( disc < 0 ) { // statements } else { // statements } } }
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ECE Application Programming: Lecture 6

30. ECE Application Programming: Lecture 6
Final notes
Next time
Continue with if statements
Switch statements
Reminders:
Program 2 due 2/5
5/11/2018
ECE Application Programming: Lecture 6